Part of your problem is that you seem to have misunderstood my original answer, so I will try to summarize the points from it, that address your question:

• Carbon dioxide has a relatively low solubility -- a saturated solution at 25°C is about 0.03 moles/liter -- so not very much of it will dissolve in water.
• Of the CO₂ that is dissolved, only about 3% will be in the form of carbonic acid. That doesn't mean that the other 97% escapes! It's still in solution. The statement that dissolved CO₂ is in the form of carbonic acid is a gross exaggeration.

If you're passing CO₂ through water in a closed vessel, it will only dissolve to the extent of 0.03 moles per liter at "standard temperature and pressure." But... if the vessel is closed the gas can't escape. So it just stays there, either as gas above the liquid or as a super-saturated solution (since you're pushing the solubility equilibrium toward more dissolved gas by increasing the pressure of gas above the liquid).

Carbonated beverages get super-saturated with CO₂ because they are pressurized with pure carbon dioxide when they are sealed. When the pressure is released, you often see the gas bubbling out of solution (which is why soda pop or carbonated mineral water fizzes on opening).

But again, the question of dissolved CO₂ forming carbonic acid (only 3% of it does) is entirely separate from the question of an overpressure of CO₂ above a saturated solution of the gas.

I hope this was helpful.

Dan Berger